ESSENTIALS OF DIAGNOSIS
History of animal exposure, or ingestion of unpasteurized milk or cheese.
Insidious onset: fatigability, headache, arthralgia, anorexia, sweating, irritability.
Intermittent and persistent fever.
Cervical and axillary lymphadenopathy; hepatosplenomegaly.
Lymphocytosis, positive blood culture, positive serologic test.
The infection is transmitted from animals to humans. Brucella abortus (cattle), B suis (hogs), and B melitensis (goats) are the main agents. Transmission to humans occurs by contact with infected meat (slaughterhouse workers), placentae of infected animals (farmers, veterinarians), or ingestion of infected unpasteurized milk or cheese. The incubation period varies from a few days to several weeks. Brucellosis is a systemic infection that may become chronic. In the United States, brucellosis is very rare. Almost all US cases are imported from countries where brucellosis is endemic (eg, Mexico, Mediterranean Europe, Spain, South American countries).
The onset may be acute, with fever, chills, and sweats, but more often is insidious with symptoms of weakness, weight loss, low-grade fevers, sweats, and exhaustion upon minimal activity. Headache, abdominal or back pain with anorexia and constipation, and arthralgias are also common. The chronic form may assume an undulant nature, with periods of normal temperature between acute attacks; symptoms may persist for years, either continuously or intermittently.
Fever, hepatosplenomegaly, and lymphadenopathy are the most common physical findings. Infection may present with or be complicated by specific organ involvement with signs of endocarditis, meningitis, epididymitis, orchitis, arthritis (especially sacroiliitis), spondylitis, or osteomyelitis.
The organism can be recovered from cultures of blood, cerebrospinal fluid, urine, bone marrow, or other sites. Cultures are more likely to be negative in chronic cases and endocarditis is often culture negative. The diagnosis often is made by serologic testing.
Brucellosis must be differentiated from any other acute febrile disease, especially influenza, tularemia, Q fever, mononucleosis, and enteric fever. In its chronic form it resembles Hodgkin disease, tuberculosis, HIV infection, malaria, and disseminated fungal infections such as histoplasmosis and coccidioidomycosis.
The most frequent complications are bone and joint lesions such as spondylitis and suppurative arthritis (usually of a single joint), endocarditis, and meningoencephalitis. Less common complications are pneumonitis with pleural effusion, hepatitis, and cholecystitis.
Single-drug regimens are not recommended because the relapse rate may be as high as 50%. Combination regimens of two or three drugs are most effective. Regimens of doxycycline (200 mg/day orally for 6 weeks) plus rifampin (600 mg/day orally for 6 weeks) or streptomycin (1 g/day intramuscularly for 2 weeks) or gentamicin (240 mg intramuscularly once daily for 7 days) have the lowest recurrence rates. Longer courses of therapy may be required to prevent relapse of meningitis, osteomyelitis, or endocarditis.